Catálogo de publicaciones - revistas

<jats:title>Foil-Forged Images</jats:title> <jats:p> X-ray diffraction is widely used to determine molecular geometries and can often distinguish mirror image isomers (enantiomers), which generally requires well-ordered crystals. <jats:bold> Herwig <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1084" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1246549">1084</jats:related-article> ) report an imaging technique to characterize enantiomers in the gas phase. A succession of ionization events were induced by passage through a carbon foil that culminated in a Coulomb explosion of mutually repelling nuclei. The trajectories of these nuclei precisely reflected the original molecular structure. </jats:p>

<jats:title>Banding Together</jats:title> <jats:p> It is important to understand how and where the Antarctic Ice Sheet and underlying ground are coupled, if we want to predict the glacial contribution to sea level rise. <jats:bold>Sergienko and Hindmarsh</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1086" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243903">1086</jats:related-article> , published online 7 November) used observations of ice surface velocities, ice surface elevations, and bed elevations to perform inverse calculations of basal shear stress. Areas of high basal stress were distributed in riblike patterns embedded in much larger areas of no basal shear stress, which may affect the rates at which ice is discharged into the ocean. </jats:p>

<jats:title>Deciphering Hepatitis C</jats:title> <jats:p> Hepatitis C virus is a major cause of liver disease and cancer. Two envelope glycoproteins, E1 and E2, form a heterodimer that facilitates infection. The envelope proteins have been difficult to crystallize, hindering vaccine development. <jats:bold> Kong <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1090" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243876">1090</jats:related-article> ) designed an E2 core glycoprotein construct and solved the crystal structure of the glycosylated protein in complex with a broadly neutralizing antibody. The host cell receptor binding site was identified by electron microscopy and mutagenesis. The findings should help in future drug and vaccine design. </jats:p>

<jats:title>Cholesterol and Cancer</jats:title> <jats:p> Obesity and high cholesterol levels are associated with an increased risk of breast cancer in post-menopausal women. <jats:bold> Nelson <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1094" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1241908">1094</jats:related-article> ) found that a specific metabolite of cholesterol, 27-hydroxycholesterol (27HC), promoted tumor growth and metastasis in mouse models of mammary cancer by serving as a partial agonist for the estrogen receptor and the liver X receptor. The most aggressive human breast cancers were found to express the highest level of the enzyme that converts cholesterol to 27HC, suggesting that 27HC produced within tumors (in addition to circulating 27HC) may contribute to tumorigenesis. </jats:p>

<jats:title>Protecting Self-Replicating RNA?</jats:title> <jats:p> The potential for self-replication makes RNA an attractive candidate as a primordial catalysis in the origin of life. Catalysis may have occurred in some kind of compartment, possibly a fatty acid vesicle. However, RNA catalysis generally requires high levels of magnesium, which are incompatible with fatty acid vesicle integrity. <jats:bold>Adamala and Szostak</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1098" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1241888">1098</jats:related-article> ) screened magnesium chelators and found that several—including citrate, isocitrate, and oxalate—could maintain the membrane stability of fatty acid vesicles in the presence of Mg <jats:sup>2+</jats:sup> . Citrate also allowed Mg <jats:sup>2+</jats:sup> -dependent RNA synthesis within protocell-like vesicles, while at the same time protecting RNA from Mg <jats:sup>2+</jats:sup> -catalyzed degradation. </jats:p>

<jats:title>Don't Ape Protein Variation</jats:title> <jats:p> Changes in DNA and messenger RNA (mRNA) expression levels have been used to estimate evolutionary changes between species. However protein expression levels may better reflect selection on divergent and constrained phenotypes. <jats:bold> Khan <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1100" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1242379">1100</jats:related-article> , published online 17 October; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1052" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1247833">Vogel</jats:related-article> </jats:bold> ) measured the differences among and within species between mRNA expression and protein levels in humans, chimpanzees, and rhesus macaques, identifying protein transcripts that seem to be under lineage-specific constraint between humans and chimpanzees. </jats:p>

<jats:title>Complexing Photosynthesis</jats:title> <jats:p> Photosynthesis operates through a series of protein complexes that harvest sunlight and turn it into chemical energy. The separate complexes—including photosystems I and II, phycobilisome antennae, and reaction centers—are understood for a number of photosynthetic organisms; however, the large-scale organization and interactions between them are less clear. Using protein cross-linking, <jats:bold> Liu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1104" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1242321">1104</jats:related-article> ) demonstrate how the individual components are organized when present as a megacomplex in the cyanobacterium <jats:italic>Synechocystis</jats:italic> PCC 6803. Time-resolved fluorescence spectroscopy indicated that the phycobilisomes transfer energy to both photosystems, which is consistent with their molecular arrangement. </jats:p>

<jats:title>It Takes a Few</jats:title> <jats:p> Persistent maintenance of long-term potentiation (LTP) of glutamatergic synapses and long-term memory requires neuronal nuclear signaling that leads to gene transcription. It is unclear whether signaling produced at a single dendritic spine can be transmitted into the nucleus to regulate gene transcription. Using two-photon glutamate uncaging in combination with two-photon fluorescence lifetime imaging, <jats:bold> Zhai <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1107" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1245622">1107</jats:related-article> ) show that induction of LTP in only three to seven dendritic spines in a hippocampal pyramidal neuron can trigger activation of nuclear extracellular signal–regulated kinase and downstream transcription factors cyclic adenosine monophosphate response element–binding protein and E26-like transcription factor-1. Thus, signaling initiated in each dendritic spine can be transmitted into the nucleus to regulate gene transcription. Furthermore, biochemical signaling in multiple dendritic branches was integrated to activate the nuclear signaling. </jats:p>

<jats:title>Remembrance of Places Past</jats:title> <jats:p> The hippocampus has two major roles in cognition. Place-responsive neurons form a context-sensitive cognitive map, firing more strongly when an animal traverses specific regions of its environment. Both humans and animals thus need the hippocampus to learn their way around novel environments. Similarly, the hippocampus is critical for our ability to remember a specific event in space and time. It has thus been suggested that the spatial and memory functions of the hippocampus reflect a common architecture. Recording from neurosurgical patients playing a virtual reality memory game, <jats:bold> Miller <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1111" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1244056">1111</jats:related-article> ) found that the recall of events was indeed associated with reinstatement of the place-firing of neurons activated as the subjects navigated through the environment. </jats:p>

<jats:title>Neuronal Activity and Dendrite Development</jats:title> <jats:p> How does the developing brain establish the correct connections? <jats:bold> Matsui <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6162" page="1114" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1244505">1114</jats:related-article> , published online 31 October) discovered an activity-dependent transcription mechanism during mouse and ferret visual cortex development that controls the direction of dendrite orientation, allowing dendrites to steer toward active axons and away from inactive axons. This mechanism enables the construction of polarized neuronal shapes for integration into neural circuits with the required finescale architecture to process subtle activity patterns, a property underlying complex behavior. </jats:p>